The use of balloon catheters for treatment in the vascular system or other lumens of the body is well known in the field of medicine. Percutaneous transluminal angioplasty (PTA) is a procedure used for the treatment of the vascular system which opens blockages in the artery. One approach which has been used in the prior art for the treatment of blockages in arteries is a dilatation balloon catheter. The dilatation balloon catheter has an inflatable balloon member proximate a distal end which is positioned across a stenosis or blockage. The catheter is inserted into the vascular system and guided to position the balloon, whereupon a fluid is injected through an inflation lumen contained within the catheter to inflate the balloon. The inflation of the balloon causes an outward expansion which opens the stenosis.
It is desirable that the dilatation balloon have a low profile while deflated to increase the ease with which the dilatation balloon can be passed through arteries having small lumens and across a stenosis. The low profile is also desirable to minimize the force required to remove the balloon catheter. Thus, low range sheath withdrawal forces for balloon catheters has always been a desirable design goal.
One approach which has been used is to fold the balloon flat prior to a treatment such as PTA. This results in two wings being formed, which may be brought together in order to reduce the overall diameter of the preinflated balloon. A sleeve may be installed around the balloon in order to hold the wings together when the balloon is in the preinflated configuration. The balloon is inflated during treatment. Once the treatment is complete, the balloon must be deflated. Often times the deflated balloon does not return to a diameter small enough to fit within a guide catheter. Often times the result of deflating the balloon by pulling a vacuum is that the balloon can flatten in a phenomena known as "winging", in which the flat lateral portions of the deflated balloon extend outward beyond the diameter of the balloon when in its inflated and preinflated condition. The presence of the wings and edges can interfere with the ease of withdrawal, both through a guide catheter and through a body vessel such as an artery. Thus, a low profile upon deflation is desirable to increase the ease of retraction by decreasing contact with the vessel walls.
Several attempts have been made in the prior art to provide a dilatation balloon having a reduced profile when in a deflated state. Campbell et al. (U.S. Pat. No. 5,458,572) disclose a balloon having an array of longitudinally and circumferentially arranged ribs. The ribs are either more stiff or less stiff than a wall of the balloon. Upon evacuation of an inflation fluid from the balloon, either portions of the wall between the ribs will collapse between the ribs, or the ribs will collapse within the wall.
Campbell et al. (U.S. Pat. No. 5,456,666) disclose a balloon formed of a continuous balloon material which has a generally cylindrical shape and four ribs formed within a body. The ribs are longitudinally and equidistantly spaced about an axis which extends from the proximal end to the distal end of the balloon. The ribs are formed of stressed balloon material. Webs of less stressed balloon material are disposed between the ribs, whereupon the ribs and the webs form the balloon which is expandable from a folded condition to an expanded condition having a diameter substantially greater than the folded condition. After completion of a treatment, the balloon is reverted back to a folded condition where the webs between the ribs collapse inwardly towards the axis.
Montano (U.S. Pat. No. 4,941,877) discloses a balloon which defines transition zones at respective ends of the balloon which have flutes which are generally longitudinally directed at an angle to a balloon axis. The balloon can assume a collapsed position in which the collapsed transition zones collapse in a preferred cross section, rather than a flat collapsed configuration.
These prior art approaches attempt to improve the folding characteristics of the balloon by utilizing either longitudinally directed ribs within the mid region of the balloon, or by utilizing generally longitudinal fluted regions defined in the transition zones. The ribs or fluted regions attempt to induce the collapse of the balloon to a predetermined configuration by creating longitudinally oriented stressed regions in the balloon material.